1. Field of the Invention
The present invention relates to a planetary gear speed reducer employed for an internal combustion engine starter or the like.
2. Description of the Related Art
FIG. 8 is a cross-sectional view illustrative of a planetary gear speed reduction starter which employs a permanent magnet as a conventional motor; and FIG. 9 is a cross-sectional view illustrative of a method for mounting a planetary gear supporting pin in a conventional planetary gear speed reduction starter.
In the drawing, an armature 1 of a DC motor serving as a rotator, is provided around an armature rotary shaft 2 as an integral part of the armature rotary shaft 2. A cylindrical yoke 3 is disposed so that it surrounds the armature 1. A front bracket 5 is connected to the end surface of the yoke 3. An internal gear 4, which constitutes the planetary gear speed reducer, is fitted inside the front bracket 5. A sun gear 6 is formed at the front end of the armature rotary shaft 2.
At the front end of the internal gear 4, a discshaped flange 4a is provided, jutting out inward; a cylindrical flange 4b is provided, jutting out to the front at the inner peripheral end of the flange 4a. A flange section 10 constructing an arm of the planetary gear speed reducer is constituted as an integral part of an output rotary shaft 11. The output rotary shaft 11 is supported by a sleeve bearing 12 serving as a bearing fitted to the flange 4b. The flange 4a restricts the thrusting movement of the output rotary shaft 11. Provided on the flange section 10 are, for example, three supporting pins 9 which are arranged at equal angle pitches on the same circumference. A planetary gear 7 is supported by a pin 9 via a bearing 8 fitted to the inner peripheral surface. In this case, each planetary gear 7 meshes with the sun gear 6 and the internal gear 4 to construct the planetary gear speed reducer.
A sleeve bearing 13 serving as a bearing is fitted in the recessed section in the rear inner peripheral surface of the output rotary shaft 11; the sleeve bearing 13 supports the front end of the armature rotary shaft 2. A steel ball 14 serving to transfer thrust load is fitted between an end of the armature rotary shaft 2 and an end of the output rotary shaft 11.
The yoke 3 has, at the front end thereof, a collar 3a which is made integral with the yoke 3 and which extends in the radial direction. The collar 3a restricts the thrusting movement of the planetary gears 7 and isolate the speed reducer and the motor unit from each other for dustproof effect. A gasket 18 is fitted between the front bracket 5, the internal gear 4, and the collar 3a to prevent the leakage of the grease applied to the meshing areas of the planetary gears 7 and the internal gear 4. A rear bracket 17 is fitted to the end surface of the opening of the yoke 3.
A plurality of auxiliary electrodes (not shown) are welded at equal angle pitches to the inner peripheral surface of the yoke 3. A plurality of arc permanent magnets 15 are disposed in such a manner that they surround the armature 1; one side surface of each permanent magnet 15 is in contact with an auxiliary electrode and a magnet holder 16 is press-fitted between the other side surface of the permanent magnet 15 and an adjoining auxiliary electrode.
There are provided as many permanent magnets 15 and auxiliary electrodes as the electrodes of the motor.
The flange section 10 formed as the integral part of the output rotary shaft 11 is furnished with a plurality of through holes 10a at equal angle pitches on the same circumference. The supporting pins 9 are machined into solid cylindrical shapes having an outside diameter which is slightly larger than the diameter of the through holes 10a. Thus, the supporting pins 9 are mounted on the flange section 10 by press-fitting them in the through holes 10a.
The operation of the conventional planetary gear speed reduction starter stated above will now be described.
Closing a key switch (not shown) energizes the armature 1 to cause the armature to produce a torque under the magnetic energization of the permanent magnet 15. The torque generated by the armature 1 is transmitted to the planetary gears 7 via the sun gear 6 of the armature rotary shaft 2. Since the planetary gears 7 are engaged with the internal gear 4, they revolve around the armature rotary shaft 2 while turning around the supporting pin 9. The torque of the armature 1 is therefore reduced in rotational speed before it is transmitted to the flange section 10 and further transmitted to the output rotary shaft 11 via the flange section 10. The torque of the output rotary shaft 11 is transmitted to a ring gear (not shown) of an internal combustion engine via a pinion (not shown) of an overrunning clutch which is fitted thereto.
As described above, the conventional planetary gear speed reducer has a problem in that the supporting pins 9 which support the planetary gears 7 are constructed separately from the flange section 10 of the output rotary shaft 11, resulting in more parts, difficulty in assembling, and higher cost.
Furthermore, the supporting pins 9 press-fitted in the through holes 10a in the flange section 10 make it difficult to vertically install the supporting pins 9 with respect to the end surface of the flange section 10, adversely affecting the engagement of the planetary gears 9 with the sun gear 6 and the internal gear 4.